I did that too, like seriously went for some exchange coins although I sold at loss on one hand and made profit on the other hand, therefore I can say some exchanges tokens are worth holding while others aren't. To confirm this, taking a glimpse on exchange tokens like Huobi and Binance for instance one can see the growth as well as the team's efforts to ensure a continuous improvement, this what makes those tokens to always bounce back after a bad or bear market. So in own opinion, exchange tokens are still altcoins but good ones in this case thus not a bad idea holding some.